Sensory Receptors Flashcards
Describe the structure of cutaneous receptors
found at the distal ends of the primary sensory axon
pacinian corpuscle
ruffinian corpuscle
Describe the 3 different types of sensory receptors
mechanoreceptor - stimulated by mechanical stimuli (pressure, stretch, deformation) gives skin sensation of touch and pressure
Proprioceptor - are mechanoreceptors in joints and muscles, they signal information about about body and limb position (touching nose)
Nociceptors - respond to painful stimuli (heat and tissue damage)
Explain the mechanism of sensory transduction in the skin
sensory receptor transduction involves ion channels opening or closing
an adequate stimulus
(form of energy to which a receptor normally responds) causes a graded membrane potential change (only a few mV) = receptor potential or graded potential
the adequate stimulus on cutaneous mechanoreceptors and proprioceptors is membrane deformation - this activates stretch-sensitive ion channels- so ions flow across the membrane and change the membrane potential locally
Describe how the receptor potential is graded by stimulus intensity
a stimulus triggers ions to flow through the membrane locally
when depolarisation reaches the area with voltage-gated ion channels (first node of Ranvier) action potentials start firing
electrodes at position 1 and 2 measure change in membrane potential
electrode 1 measures receptor potentials - electrode 2 measures action potential
lowest stimulus intensity produces no action potentials
highest stimulus intensity produces most action potentials
Explain the concept of frequency coding
- larger stimulus
- causes larger receptor potential
- higher frequency of action potentials
for some mechanoreceptors - if stimulus persists, AP’s persist
for others, continuous mechanical stimulation causes a drop off in AP’s - your brain then can process now or changing events
(eg, you feel your clothes when they go on- less when they are on)
Describe the structure and function of the muscle spindle
function - monitor muscle length and rate of change of muscle length, control reflexes and voluntary movements
structure - extrafusal fiber, intrafusal fiber, central region lacks myofibrils, gamma motor neurons for CNS, sensory neuron
y motor neuron activation contracts the ends of the musclespindles
Describe the structure and function of intrafusal fiber
nuclear bag fibres - bag shaped with nuclei collected together
nuclear chain fibres - nuclei lined up in a chain - muscle fibres are multi nucleated
primary endings from afferent nerves wrap around the centre of intrafusal fibres: they form annulospiral endings
the ends of intrafusal fibres containing contractile sacromeres - but the central area has no contractile element
gamma (y) motorneurons innervate and cause contraction of the contractile ends of the intrafusal fibres - when they fire the two ends contract and shorten but the central area does not getting stretched out
Describe the Pacinian corpuscle
comprises a myelinated nerve with a naked nerve ending
enclosed by a connective tissue capsule of layered membrane lamellae
each layer is separated by fluid
Describe how the Pacinian corpuscle responds to stimulus
- a mechanical stimulus deforms the capsule and the nerve endings
- this stretches the nerve ending and opens ion channels
- Na ion influx causes local depolarisation - a receptor/generator potential
- APs are generated and fire where myelination begins (because regenerative Na ion channels cluster at nodes Ranvier)
- Brain detects stimulus (ON)
fluid rapidly redistributes within capsules lamellae, this spreads the stimulus impact out laterally - minimising deformation
downward force causing mechanical stretch to nerve endings stop - AP’s stop firing
as stimulus is withdrawn - capsule lamellae spring back and AP’s fir again
Describe the structure and function of the Golgi tendon organ
function - monitor tension on tendons, tension is produced by muscle contraction, so monitoring muscle tension
structure - collagen fibre, capsule, tendon, afferent neuron, sensory neuron
nerve endings of GTO mingle with the tendon bundles at the end of muscles
muscles have to develop tension by contracting to stretch the tendon (inelastic)
Describe the receptive field
a somatic sensory neuron is activated by stimuli in a specific area called the receptive field
touch-sensitive neuron in the skin responds to pressure within a defined receptive field
Describe lateral inhibition
stimulus - primary neuron response is proportional to stimulus strength - pathway closest to stimulus inhibits neighbours - inhibition of lateral neurons enhances perception of stimulus
receptors at edge of stimulus are more strongly inhibited than receptors near centre
enhances the contrast between relevant and irrelevant information (sharpens or cleans up sensory information )
Describe how muscle stretch stimulates the spindle stretch receptors
stretch sensitive ion channels open, create a local generator potential, this causes regenerative action potentials in the 1a afferent fibres
- resting AP frequency depends on length of L0
- during stretch from L0 to L1, increase in AP frequency is proportional to velocity of stretch (slope of the line)
- increased AP frequency at new steady state … L1 > L0
